Recently, a plasma display panel (hereinafter abbreviated to “PDP”) display device that utilizes the light emission of the phosphor excited by the ultra-violet ray has been commercially available. Moreover, as a thin flat-type image display device that utilizes the light emission of the excited phosphor, there is also, for example, the FED (Field Emission Display) which utilizes the light emission of the excited phosphor induced by irradiating, with the electron beam, the phosphor from the cold cathode electron source in which a large number of electron emitting elements are arranged in a matrix manner (two dimensionally).
Generally, not only the PDP display device but also all image display devices utilizing the light emission of the phosphor has the problem as follows. That is, if the static image with a high luminance level is displayed for a long time, the phosphor is degraded, and consequently, the difference in luminance (luminance difference) is caused between that part and other parts, that is, a so-called image retention occurs.
For the prevention of the image retention, there is a process as disclosed in JP-A No. Hei 5-344371, in which the displayed image remains unchanged for a predetermined time or longer, the image is regarded as a static image, and the luminance level of the entire display screen is lowered.
Moreover, JP-A No. 2000-227775 discloses a method in which when a static image is disclosed on the screen for a predetermined time or longer, the entire screen is moved by several dots to an almost imperceptible extent.
Furthermore, JP-A No. 2002-351442 discloses a method in which, in the case where both the moving image and the static image are displayed on the screen, the static image part is distinguished from the entire screen, and when the static image part remains unchanged for a predetermined time or longer, the luminance level only in the static image part is lowered.